In response to increases in the use of methylenedioxymethamphetamine (MDMA) and other "club drugs" among young people, the National Institute on Drug Abuse issued a "Club Drug" Alert in December, 1999, to warn the nation of the dangers associated with these drugs. Despite our knowledge of the risks associated with club drug use, little is known about the people who use these substances, including initiation patterns, substance abuse practices, health problems related to drug abuse, perceived need for health services, or HIV/STD sex risk behaviors. The overall objective of this proposal is to produce a longitudinal epidemiologic study of MDMA and other club drug users that is informed by ethnographic research. Using a natural history research design, 480 active MDMA users recruited in Columbus, Ohio, will complete a structured assessment every six months for three years. The Specific Aims are to: 1. Describe key dimensions in club drug use and risky sexual practices among young adults in Columbus, Ohio, using ethnographic/qualitative methods; 2. Describe the characteristics of 480 active MDMA users recruited in Columbus, Ohio, and conduct preliminary analyses focusing on substance abuse practices, sex risk behaviors, and psychological problems; 3. Describe and analyze changes in MDMA use and the relationship between MDMA and other drug use practices among 480 young adults over a three-year period; 4. Determine the incidence of substance abuse-related problems and resulting health service utilization over three years; 5. Identify the factors that predict risky sexual behaviors among 480 MDMA users over a three-year period; and 6. Describe the club drug use practices of 40 minors in recovery using qualitative methods and identify the complications of conducting research with active club drug users under 18. The proposed research is significant because little is known about club drug users or the nature and extent of risky sexual behaviors among this population. It is innovative because the use of ethnographic and quantitative methods will provide a well-rounded epidemiologic understanding of how club drug use and sex risk behaviors interface over time among young people in the Midwest. The results can inform future sex risk-reduction interventions as well as club drug prevention and treatment initiatives.